5. Abstract Base Classes (ABCs)

These examples demonstrate how abc can be used to enforce method implementation in subclasses, ensure adherence to interfaces, and provide a clear structure for abstract behavior.

1. Basic Abstract Base Class

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from abc import ABC, abstractmethod

class Animal(ABC):
    @abstractmethod
    def make_sound(self):
        pass

class Dog(Animal):
    def make_sound(self):
        return "Woof!"

dog = Dog()
print(dog.make_sound())  # Output: Woof!

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2. Abstract Class with Multiple Methods

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from abc import ABC, abstractmethod

class Shape(ABC):
    @abstractmethod
    def area(self):
        pass

    @abstractmethod
    def perimeter(self):
        pass

class Rectangle(Shape):
    def __init__(self, width, height):
        self.width = width
        self.height = height

    def area(self):
        return self.width * self.height

    def perimeter(self):
        return 2 * (self.width + self.height)

rect = Rectangle(4, 5)
print(rect.area())       # Output: 20
print(rect.perimeter())  # Output: 18

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3. Preventing Instantiation of Abstract Classes

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from abc import ABC, abstractmethod

class Vehicle(ABC):
    @abstractmethod
    def start_engine(self):
        pass

# vehicle = Vehicle()  # Raises TypeError: Can't instantiate abstract class Vehicle

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4. Partially Implemented Abstract Base Class

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from abc import ABC, abstractmethod

class Appliance(ABC):
    @abstractmethod
    def turn_on(self):
        pass

    def plug_in(self):
        print("Appliance is now plugged in.")

class WashingMachine(Appliance):
    def turn_on(self):
        print("Washing Machine is now running.")

machine = WashingMachine()
machine.plug_in()  # Output: Appliance is now plugged in.
machine.turn_on()  # Output: Washing Machine is now running.

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5. Abstract Properties

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from abc import ABC, abstractmethod

class Employee(ABC):
    @property
    @abstractmethod
    def salary(self):
        pass

class Manager(Employee):
    def __init__(self, base_salary):
        self._salary = base_salary

    @property
    def salary(self):
        return self._salary

manager = Manager(100000)
print(manager.salary)  # Output: 100000

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6. Abstract Base Class with Class Methods

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from abc import ABC, abstractmethod

class Database(ABC):
    @classmethod
    @abstractmethod
    def connect(cls):
        pass

class MySQLDatabase(Database):
    @classmethod
    def connect(cls):
        print("Connecting to MySQL database...")

MySQLDatabase.connect()  # Output: Connecting to MySQL database...

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7. Combining Abstract Base Class with Interfaces

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from abc import ABC, abstractmethod

class Flyable(ABC):
    @abstractmethod
    def fly(self):
        pass

class Bird(Flyable):
    def fly(self):
        print("Bird is flying.")

bird = Bird()
bird.fly()  # Output: Bird is flying.

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8. Multiple Abstract Base Classes

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from abc import ABC, abstractmethod

class Swimmable(ABC):
    @abstractmethod
    def swim(self):
        pass

class Flyable(ABC):
    @abstractmethod
    def fly(self):
        pass

class Duck(Swimmable, Flyable):
    def swim(self):
        print("Duck is swimming.")

    def fly(self):
        print("Duck is flying.")

duck = Duck()
duck.swim()  # Output: Duck is swimming.
duck.fly()   # Output: Duck is flying.

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9. Abstract Base Class with __init__

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from abc import ABC, abstractmethod

class Vehicle(ABC):
    def __init__(self, brand):
        self.brand = brand

    @abstractmethod
    def drive(self):
        pass

class Car(Vehicle):
    def drive(self):
        print(f"{self.brand} car is driving.")

car = Car("Tesla")
car.drive()  # Output: Tesla car is driving.

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10. Using Abstract Base Class for Type Checking

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from abc import ABC, abstractmethod

class Media(ABC):
    @abstractmethod
    def play(self):
        pass

class Video(Media):
    def play(self):
        print("Playing video.")

class Audio(Media):
    def play(self):
        print("Playing audio.")

def play_media(media: Media):
    media.play()

video = Video()
audio = Audio()

play_media(video)  # Output: Playing video.
play_media(audio)  # Output: Playing audio.